District 3 begins reviewing speed limits near cities

The Idaho Legislature this year delegated authority to ITD for setting speed limits on state highways within local jurisdictions, such as cities and in counties. The law became effective July 1. As a result, the traffic engineers have begun assessing existing speed limits to determine whether prevailing speed limits are appropriate or if the speed limits should be increased or decreased. Decisions are made after traffic studies and adhere to Federal Highway Administration's "85th percentile," guidelines. (See story below)

District 3 engineers already determined that speed limits on Idaho 44 at Middleton, and U.S. 20 (Chinden Road) in Boise should be modified. Crews began implementing those changes this week.

To increase safety and improve traffic flow, the speed limit on several sections of Idaho 44 in Middleton will be changed Tuesday morning (July 31) as soon as crews can change the signs. This is in accordance with state law giving ITD the authority to set limits on all state highways and interstate routes.

ITD met with city officials Friday morning (July 27). The city requested that ITD review speed limits and supports the change.

Here are the areas of Idaho 44 affected by the new speed limits.

  • The speed limit from Hartley Lane to midway between Eaton Road and Cemetery Road will go from 35 mph to 40 mph
  • From that point to Cemetery Road will be 35 mph
  • From Cemetery Road to Dewey Avenue will be posted at 25 mph
  • From Dewey Avenue to N. Middleton Road will be posted at 35 mph

The speed limit is being changed to comply with a June 2012 study of the speeds that motorists already drive on the highway.
The posted limit is a maximum speed when there are no obstacles or distractions and the pavement is dry. With icy, snow-covered or slick roads, it is always prudent to travel slower than the allowed posted limit. The speed-limit guideline is safe and prudent for the conditions.

"Speed-limit signs cannot replace common sense," said ITD's Southwest Idaho Traffic Manager, Kevin Sablan. "They are intended to supplement - not substitute for - the driver's judgment."

ITD traffic engineers set the limit at the speed at which 85 percent of the traffic is driving to determine a safe and reasonable speed for a given road section, in accordance with federal safety guidelines. According to research, setting a speed limit according to that 85th percentile results in the fewest crashes.

Reducing a speed limit does not necessarily result in safer driving conditions. Reducing the limit below the warranted speed can actually be hazardous and unsafe. Studies show that merely reducing a speed limit has little effect on the speed at which motorists will travel. Furthermore, no published research has established a direct relationship between lower posted speed limits and crash frequency.

Limits help determine a reasonable speed for a particular road under ideal weather conditions. Speed Limits are imposed to assist Idaho law enforcement, and enforcement of the limits by them is essential. Limits encourage better traffic flow by reducing the variances in speed from one vehicle to the next, enhancing free-flowing movement.

In determining speed limits, the investigation involves determining the design of the road and its immediate environment. Engineers analyze factors such as lane width, pavement type and condition of the road. They also look at terrain, parking conditions, residential development along the road and the number, width and types of entrances and intersecting streets.

Published 8-3-2012